The invention is based on a microswitch according to the preamble of patent claim 1. Such a switch is fitted on a substrate and has a contact arrangement provided for switching a current on or off and an electrically actuable drive for a moveable contact piece of the contact arrangement. By means of the drive, which may operate for example electrostatically, electro-magnetically, piezoelectrically or thermally, the moveable contact piece is moved from a switch-off position to a switch-on position, or vice versa, a contact carrier which can be elastically deformed by bending providing for a restoring force.
The microswitch can be produced by known methods of semiconductor technology or comparable methods of micromachining and is therefore particularly suitable for integration with other semiconductor-technological devices, in particular integrated circuits.
In addition, the microswitch has extremely fast response times in comparison with conventional electromagnetic switches on account of the small moving masses. At the same time, the required switching powers are very low, so that considerable power savings can be achieved in particular in the case of multiple use in a relatively large circuit.
With the preamble of patent claim 1, the invention refers to a prior art of microswitches as is specified for example in U.S. Pat. No. 5,638,946A. A microswitch described in FIG. 4 of this document contains a substrate of plate-type design, the two electrically conductive end parts 96a, 96b of a flexible contact carrier which is bent in a U-shaped manner being fixed on the surface of said substrate. A bridge contact piece 99 is fitted on the contact carrier in an electrically insulated manner. Furthermore, two stationary contact pieces 94 and 94xe2x80x2 and two control electrodes 92a and 92b are arranged on the substrate surface. During the operation of this switch, an electric field is applied to the control electrode 92a and the end part 96a or to the control electrode 92b and the end part 96b, which electric field bends the contact carrier in the direction of the substrate surface. The bridge contact 99 then short-circuits the two contact pieces 94, 94xe2x80x2 and current can then flow from the contact piece 94 via the bridge contact 99 to the contact piece 94xe2x80x2. The electric field holds the bridge contact in the switch-on position counter to the spring force of the contact carrier. In order to open the switch, the electric field is reduced by changing the voltage of the control electrode 92a or 92b and the bending of the contact carrier is reversed with the contacts being isolated. The force applied by the drive is comparatively low. Moreover, the switch opens in an undesirable manner in the event of an unintentional weakening or in the event of failure of the electric field.
The invention, as it is defined in the patent claims, achieves the object of specifying a microswitch of the type mentioned in the introduction which can be operated with a low expenditure of force and energy and which at the same time is distinguished by high operational reliability.
In the case of the microswitch according to the invention, the flexible contact carrier fixed at both ends is designed such that it can be deformed parallel to the plate-type substrate and has two stable positions which can be reached by elastic deformation of the contact carrier, of which positions one is assigned to the switch-off position and the other to the switch-on position. A switch drive which effects the transition from the switch-off position to the switch-on position and vice versa from the switch-on position to the switch-off position therefore only has to apply a comparatively low deformation energy during a switching operation. Since reliable contact-making or reliable contact isolation is ensured by the two stable positions, a high operational reliability of the switch is ensured even without additional securing means or without an additional force, as is brought about for instance by an electric field. This advantageously makes use of the fact that one of the two stable positions is achieved by shaping a contact carrier designed as a symmetrical antinode as early as during the production of the switch, for example by deep reactive ion etching (DRIE). At the same time, it has been recognized that the other of the two stable positions can be achieved if the symmetrical antinode is converted into an asymmetrical antinode by elastic deformation. Since the contact carrier executes a relatively large swing during the transition from one stable position to the other, an isolating path which is formed in the event of switch-off and is defined by the swing, between the opened contacts of the switch, is distinguished by high dielectric strength.
An asymmetrical antinode can be achieved if the stationary contact piece, at the point at which it touches the moveable contact piece, has a smaller distance from one of the two ends of the contact carrier than from the other end thereof. In this case, however, the value of a position coordinate taken parallel to the connecting path, between the two contact carrier ends, at the location of the contact point should expediently be between 0.08 and 0.48 times the length of the connecting path, since otherwise the positional stability is reduced to an excessively great extent. In order to obtain a large isolating path and thus a high dielectric strength, in the case of a symmetrical antinode lying above the connecting path, the contact point should be arranged on or below the connecting path.
If the isolating point of the switch is bounded merely by the stationary and the moveable contact piece, then the contact carrier should be designed to be electrically conductive at least between one of its two ends and the moveable contact piece. An additional current feed to the moveable contact piece can then be obviated. By contrast, if the moveable contact piece is designed as a bridge contact, and if a further stationary contact piece is arranged on the substrate, which contact piece, like the other stationary contact piece, makes contact with the bridge contact in the switch-on position, then the contact carrier should be electrically insulated from the substrate or the bridge contact should be electrically insulated from the contact carrier.
In an embodiment of the microswitch according to the invention which is designed with particular operational reliability, the switch drive has two mutually independently displaceable mechanical actuation elements, of which one acts on the contact carrier in the event of switch-on with a force which is necessary in order to achieve the switch-on state through elastic deformation of the contact carrier and the other acts on the contact carrier in the event of switch-off with a force which is necessary in order to achieve the switch-off state through elastic deformation of the contact carrier. In the displacement direction, at least one of the two actuation elements should form an acute angle with the tangential plane at the bearing point of this actuation element on the contact carrier. This is because the deformation work in the event of switch-on or switch-off can then be done with a comparatively small drive force. A particularly suitable drive for this purpose with a large swing in conjunction with a comparatively low force is a drive having two electrostatically acting comb structures, a respective one of which interacts with a respective one of the two actuation elements. Such a drive can be worked out from the substrate together with the contact carrier in an economically advantageous manner, preferably by means of an ion etching method.